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Polypropylene blends with polyhedral oligomeric silsesquioxanes (POSS) bearing different alkyl groups were investigated to elucidate the effect of the alkyl group length on the mechanical behavior of the blends. In particular, blends of polypropylene (PP) with either octamethyl-POSS, octaisobutyl-POSS, or isooctyl-POSS were studied. Differential scanning calorimetry evidenced only minor changes in the degree of crystallinity compared to neat PP. Uniaxial tensile tests showed that the incorporation of octamethyl-POSS induces an increase in Young’s modulus and a reduction of the yield strength in comparison with unfilled PP. By contrast, upon the incorporation of octaisobutyl-POSS and isooctyl-POSS, both Young’s modulus and the yield strength were found to decrease by increasing the POSS content. It is suggested that POSS behave as particles having a siliceous hard-core surrounded by a hydrocarbon soft-shell, which limits the stress transfer from the matrix to the core in dependence on the length of the alkyl groups. Finally, the essential work of fracture method was employed to study the fracture behavior of octamethyl-POSS/PP blends, with different POSS contents (0, 3, and 10 wt %)

Several diseases would benefit from prolonged drug release provided by systems retained in the stomach for extended time periods. Expandable gastroretentive devices are administered in a collapsed configuration enabling swallowing and regain in situ their native shape having larger spatial encumbrance, thus hindering voidance through the wide open pylorus. An expandable system for gastric retention was here proposed relying on the shape memory behavior of pharmaceutical-grade poly(vinyl alcohol). Different original configurations to be recovered upon exposure to aqueous fluids at 37 °C, potentially enabling gastric retention, were conceived. Prototypes containing allopurinol were directly manufactured by fused deposition modeling or shaped by purposely-designed templates from hot melt extruded rods immediately after production. Various temporary shapes, in principle suitable for administration, were programmed by manual deformation of samples by means of specific templates, under defined temperature conditions. In 0.1N hydrochloric solution at 37 °C, the prototypes recovered their original shape, reaching the desired spatial encumbrance within few minutes. Release from the samples, although of relatively short duration, was independent of the original shape and processing undergone, and was noticeably slowed down by application of Eudragit RS/RL-based coatings.

Retentive device for intravesical drug delivery based on water-induced shape memory response of poly(vinyl alcohol): design concept and 4D printing feasibility

In this work, melt spinning experiments were tentatively used for the determination of the elongational viscosity of polymer melts at different levels of tensile strain and strain rate. The materials examined were two high-density polyethylene grades for blow moulding with similar number-average molecular mass but different polydispersity index. The data from melt spinning tests were compared with transient extensional viscosity data obtained by uniform isothermal tensile tests, performed by means of an extensional rheometer, as well as with those produced by converging flow tests (Cogswell model). The results showed that for high strain and strain rate levels, the melt spinning experiments provide elongational viscosity data quite close to the transient extensional viscosity values obtained from the tensile tests

This work investigated the mechanical behavior of POSS-modified polyamide 6 (PA6), containing PA6 chains terminated at one end with aminopropyl-heptaisobutyl POSS. Three systems with different POSS contents (5.4, 10.8, and 16.2 wt %), each characterized by a specific molecular mass, and the corresponding PA6 neat polymers were examined. The materials were first subjected to morphological and calorimetric analysis by wide-angle X-ray diffraction and differential scanning calorimetry, respectively. Tensile tests, performed on the samples in wet conditions, showed that stiffness, strength, and ductility were appreciably modified by the presence of POSS in the polymeric chains. The relationships among these effects and the microstructural characteristics of the systems also were analyzed

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The shape memory behavior of polymers derives from a combination of their molecular architecture and thermomechanical history. In this study, several epoxies with various network architectures were prepared using mixtures of a diepoxide resin, a monoepoxide resin, and an aliphatic diamine hardener. A nonconventional cold-working programming, carried out below T-g, was employed to set the materials in a temporary configuration and allowed to fix considerable amounts of the applied strain. The shape memory behavior was evaluated through transient heating and isothermal recovery tests. All the resins are capable of complete recovery, which occurs as a sequence of an early process taking place below T-g and a major one close to T-g, which acted as the switching temperature (T-switch). The proximity of the deformation temperature to T-g influenced the amount of strain recovered within each process. It was shown that resins with different structures, although presenting similar T-switch, may have different recovery kinetics, and the roles of the network density and the chain stiffness on the recovery rate were evidenced